This invention relates to an optical sensor device which can be coupled to a window pane, in particular to a windshield of a motor vehicle.
Such sensor devices chiefly are used as rain sensors in motor vehicles for automatically actuating the wipers and as light sensors for controlling the vehicle lighting. The use of classical lenses for influencing the optical path, such as the lenses inclined towards the windshield of the rain sensor disclosed in EP 1 068 112 B1, requires a relatively large packaging space.
As known e.g. from WO 03/026937 A1, smaller constructions are possible by using holographic structures. These sensors are based on the principle of the diffraction of light by means of diffractive elements and therefore have the principal disadvantage of a much smaller yield of useful light and a higher sensitivity to extraneous light.
As regards an optical sensor device, DE 196 08 648 C1 proposes to form the light entrance and emergence surfaces of the light guide unit as Fresnel lenses. But since the surfaces of the light guide, in which the lenses are formed, are arranged perpendicular to the surface of the window pane, the required packaging space of this device is very large.